Unmanned aerial vehicle and landing method thereof

ABSTRACT

An unmanned aerial vehicle (UAV) and a landing method thereof are provided. The landing method includes the following steps. Firstly, a depth image of a scene is obtained. Next, a landing position is determined in accordance with the depth image. Next, a height information of the landing position is obtained. Next, a plurality of relative distances of the landing gears relative to the landing position are adjusted in accordance with the height information to make the relative distances substantially the same. Then, the UAV lands on the landing position.

BACKGROUND OF THE INVENTION

This application claims the benefit of People's Republic of Chinaapplication Serial No. 201610152609.X, filed Mar. 17, 2016, thedisclosure of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to an unmanned aerial vehicle and a landing methodthereof, and more particularly to an unmanned aerial vehicle capable oflanding steadily even on a relatively steep terrain and a landing methodthereof.

DESCRIPTION OF THE RELATED ART

The unmanned aerial vehicle (UAV) refers to an aerial vehicle withoutany pilot therein. The UAV can fly via control or fly automatically, andland on different environments to perform a number of tasks. However, ifthe place where the UAV is going to land belongs to a relatively steepterrain, such as a stairway, a bumpy ground, a steep cliff and so onthat have a larger level drop, it is possible to cause the UAV to toppleover or even drop and be broken when the UAV lands due to the level dropof the terrain.

SUMMARY OF THE INVENTION

The invention is directed to a UAV and a landing method thereof. The UAVwill first search for a suitable landing position before landing, so asto prevent itself from toppling over resulted from the larger level dropwhile being landing.

According to one aspect of the present invention, a landing method of aUAV is provided. The method includes the following steps. Firstly, adepth image of a scene is obtained. Next, a landing position isdetermined in accordance with the depth image. Next, a heightinformation of the landing position is obtained. Next, a plurality ofrelative distances of the landing gears relative to the landing positionare adjusted in accordance with the height information to make therelative distances substantially the same. Then, the UAV lands on thelanding position.

According to another aspect of the present invention, a UAV is provided.The UAV includes a fuselage, a plurality of landing gears disposed onthe fuselage, a 3D image recognition system disposed on the bottom ofthe fuselage for obtaining a depth image of a scene, a processing unitcoupled to the 3D image recognition system for determining a landingposition in accordance with the depth image, and a plurality of distancesensing units respectively disposed on the landing gears for obtaining aheight information of the landing position. The processing unit adjustsa plurality of relative distances of the landing gears relative to thelanding position in accordance with the height information to make therelative distances substantially the same, and lands the UAV on thelanding position.

The above and other aspects of the invention will become betterunderstood with regard to the following detailed description of thepreferred but non-limiting embodiment(s). The following description ismade with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a UAV according to an embodiment of thepresent invention.

FIG. 2 is a block diagram of the UAV according to an embodiment of thepresent invention.

FIG. 3 is a flow chart of a landing method of the UAV according to anembodiment of the present invention.

FIG. 4 is a part of flow chart of the landing method of the UAVaccording to another embodiment of the present invention.

FIG. 5 is a schematic diagram of a 2D image according to anotherembodiment of the present invention.

FIGS. 6A-6C are schematic diagrams showing the landing of the UAVaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments are provided and described in detail as follow. Theembodiments are merely described for being an example, but do not limitthe scope of the present invention. In addition, in order to clearlyshow the technical features of the present invention, parts of elementsare omitted in the drawings of the embodiments.

Refer to FIG. 1. FIG. 1 is a perspective view of a UAV 100 according toan embodiment of the present invention.

The UAV 100 includes a fuselage 110, a plurality of landing gears 121,122, 123 and 124, a plurality of whirl wing structures 130, a 3D imagerecognition system 140 and a plurality of distance sensing units 150.The 3D image recognition system 140 may be disposed on the bottom of thefuselage 110 for obtaining a depth image of a scene, and may be capableof capturing a 2D image of the scene. The landing gears 121, 122, 123and 124 and the whirl wing structures 130 are assembled together anddisposed on the fuselage 110. Each of the landing gears 121, 122, 123and 124 may respectively correspond to one of the whirl wing structures130. The distance sensing units 150, such as the infrared sensors, areused to obtain a height information of the landing position andrespectively disposed on the landing gears 121, 122, 123 and 124. Thelanding gears 121, 122, 123 and 124 with a telescopic function may bespecifically designed as screw rods, sleeves and so on, which arecontrolled to lengthen or shorten by an element such as a steppingmotor. The numbers of the landing gears, the whirl wing structures andthe distance sensing units of the UAV 100 as shown in FIG. 1 are allfour, but the present invention does not limit thereto. The numbers ofthe landing gears, the whirl wing structures and the distance sensingunits may be three or more than four.

Refer to FIG. 2. FIG. 2 is a block diagram of the UAV 100 according toan embodiment of the present invention.

The UAV 100 further includes a processing unit 202 and a storage unit206. The storage unit 206 is used to store the height information of thelanding position obtained from the distance sensing units 150, such as amemory. The processing unit 202 is coupled to the 3D image recognitionsystem 140 and the storage unit 206 for determining a landing positionin accordance with the depth image obtained from the 3D imagerecognition system 140. In addition, the processing unit 202 may furthercontrol and adjust the length of each of the landing gears 121, 122, 123arid 124 respectively in accordance with the height information storedin the storage unit 206. The processing unit 202 may be, for example, amicroprocessor or a microcontroller.

Refer to FIG. 3. FIG. 3 is a flow chart of a landing method of the UAVaccording to an embodiment of the present invention. In the presentembodiment, the UAV 100 of FIGS. 1-2 is exemplarily used for describingthese steps of flow process.

In step S1, the 3D image recognition system 140 obtains a depth image ofa scene. The 3D image recognition system 140 may capture 2D images ofdifferent scenes, and perform processing to the 2D images to obtain adepth information of the 2D image, so as to obtain the depth image ofthe scene.

Refer to FIGS. 4 and 5. FIG. 4 is a part of flow chart of the landingmethod of the UAV according to another embodiment of the presentinvention. FIG. 5 is a schematic diagram of a 2D image according toanother embodiment of the present invention.

For instance, in step S11, the image capturing unit in the 3D imagerecognition system 140 (such as a camera or a video camera) captures a2D image I of the scene. The image capturing unit may capture the 2Dimage I of the scene in accordance with different shooting angles (e.g.,swinging the lens of the image capturing unit) and shooting ranges(e.g., controlling the lens of the image capturing unit to zoom in orzoom out).

Next, in step 512, the 3D image recognition system 140 divides the 2Dimage I into a plurality of regions, such as region A1, region A2,region A3 and region A4. In one embodiment, the number of the regionsbeing divided may correspond to the number of the landing gears of theUAV.

In step S13, the 3D image recognition system 140 obtains depth values ofall pixels in each of the regions A1, A2, A3 and A4. For example, inregion A1, there are pixels A11, A12, . . . , A1 n contained therein.The 3D image recognition system 140 may depend on the color depth ineach of the pixels A11, A12, . . . , A1 n to recognize and obtaincorresponding depth values D1 n of all the pixels A11, A12, . . . , A1n, wherein n is an integer equal to or larger than 1.

In step S14, the 3D image recognition system 140 calculates averagedepth values respectively corresponding to each of the regions A1, A2,A3 and A4 to obtain the depth image. In case of region A1 the 3D imagerecognition system 140 calculates average values of all the depth valuesD1 n to obtain an average depth value D1 of region A1. On this basis,the 3D image recognition system 140 respectively calculates averagedepth values D2, D3 and D4 of the regions A2, A3 and A4, so as to obtainthe depth image of the captured scene.

Refer to FIG. 3. After the step S1 of obtaining the depth image of thescene, the method proceeds to step S2. In step S2, the processing unit202 determines a landing position in accordance with the depth image.

Refer to FIG. 4. In step S21, the processing unit 202 obtains a maximumaverage depth value D_(MAX) and a minimum average depth value D_(MIN)from the average depth values D1, D2, D3 and D4 of the regions A1, A2,A3 and A4, respectively. For instance, among the four regions A1, A2, A3and A4, the average depth value D3 of the region A3 is the maximum,while the average depth value D1 of the region A1 is the minimum. As aresult, D3 is the maximum average depth value D_(MAX), and D1 is theminimum average depth value D_(MIN).

In step S22, the processing unit 202 subtracts the minimum average depthvalue D_(MIN) from the maximum average depth value D_(MAX) to obtain adifference value D_(DIFF)=D3−D1.

In step S23, the processing unit 202 determines whether the differencevalue D_(DIFF) is smaller than a threshold value. When the processingunit 202 determines that the difference value D_(DIFF) is smaller thanthe threshold value, the method proceeds to step S24, that is, theprocessing unit 202 determines to land the UAV on the landing position.When the processing unit 202 determines that the difference valueD_(DIFF) is larger than the threshold value, the processing unit 202determines the 3D image recognition system 140 to re-obtain a depthimage of a scene, that is, the method proceeds back to step S1 to searchfor a suitable landing position.

In one embodiment, the threshold value of step S23 may be a maximumtelescopic length of each of the landing gears 121, 122, 123 and 124.That is, before landing, the UAV will first search for a suitablelanding position where the UAV can land steadily. If the first foundlanding position has a level drop that is larger than a maximumtelescopic length of each of the landing gears 121, 122, 123 and 124 sothat the UAV cannot keep a balance or may even topple over, the UAV willcontinue to find another landing positions.

Refer to FIG. 2. After the step S2 of determining the landing positionin accordance with the depth image, the method proceeds to step S3. Instep S3, the distance sensing units 150 obtain a height information ofthe landing position, and store the height information in the storageunit 206.

In one embodiment, when determining to land the UAV on the landingposition, the processing unit 202 orders the UAV to fly to the landingposition, and aims each of the landing gears 121, 122, 123 and 124 tocorrespond to each of the regions A1, A2, A3 and A4. In this embodiment,the distance sensing units 150 are, for example, infrared sensors forsensing distance. The distance sensing units 150 are respectivelydisposed in the landing gears 121, 122, 123 and 124 for obtaining aheight information of the landing position corresponding to each of theregions A1, A2, A3 and A4. The infrared sensor includes an emitting endfor emitting an infrared light to the ground and a receiving end forreceiving the infrared light reflected from the ground. During thetraveling of the infrared light, an energy attenuation will begenerated. The infrared sensors may respectively obtain current heightsrelative to the ground of each of the landing gears 121, 122, 123 and124 according to the energy attenuation, so as to obtain the heightinformation of the landing position, and store the height information inthe storage unit 206.

Next, after the step S3 of obtaining the height information of thelanding position, the method proceeds to step S4. In step S4, theprocessing unit 202 adjusts a plurality of relative distances of thelanding gears 121, 122, 123 and 124 relative to the landing position inaccordance with the height information to make the relative distancessubstantially the same.

In one embodiment, the processing unit 202 may lengthen or shorten thelength of each of the landing gears 121, 122, 123 and 124 respectivelyin accordance with the height information stored in the storage unit 206to make the relative distances of the landing gears 121, 122, 123 and124 substantially the same.

Next, after the step S4 of adjusting the relative distances of thelanding gears 121, 122, 123 and 124 relative to the landing position,the method proceeds to step S5. In step S5, the processing unit 202orders the UAV 100 to land on the landing position. Because the relativedistances of the landing gears 121, 122, 123 and 124 relative to thelanding position have been adjusted substantially the same in the stepS4, the processing unit 202 may order the UAV 100 to land in such astraightly downward way that the landing gears 121, 122, 123 and 124 cantouch the ground simultaneously to keep the balance during landing.

FIGS. 6A-6C are schematic diagrams showing the landing of the UAVaccording to an embodiment of the present invention. FIGS. 6A-6C areexemplarily used for describing the landing process of the steps S3 toS5. In the present embodiment, the UAV 100 of FIGS. 1-2 is exemplarilyused for describing these steps of landing process.

Refer to FIG. 6A. When the UAV 100 confirms a landing position 10, thedistance sensing units 150 respectively disposed on the landing gears121, 122 (not shown), 123 and 124 obtain a height information of thelanding gears 121, 122, 123 and 124 on the landing position 10. Forexample, heights relative to the ground H1, H3 and H4 of each of thelanding gears 121, 123 and 124 measured by the distance sensing units150 on the landing gears 121, 123 and 124 are 140 cm, 200 cm and 160 cm,respectively. The heights relative to the ground H1, H3 and H4 are usedas the height information of the landing position 10.

Refer to FIG. 6B. After the distance sensing units 150 obtain the heightinformation of the landing position 10, the processing unit 202 dependson the height information to shorten the length L1 of the landing gear121 by 10 cm, and respectively lengthen the lengths L3 and L4 of thelanding gears 123 and 124 by 50 cm and 10 cm. Therefore, the relativedistances of the landing gears 121, 123 and 124 relative to the landingposition 10 are adjusted to be equal to each other (i.e., 150 cm).

Refer to FIG. 60. After adjusting the relative distances of the landinggears 121, 123 and 124 relative to the landing position 10, theprocessing unit 202 controls the UAV 100 to fly downwards by 150 cm onthe landing position 10. Finally, the landing gears 121, 123 and 124 maytouch the ground simultaneously without losing balance when the UAV 100lands.

In the landing method of the UAV disclosed in above embodiment of thepresent invention, the UAV will first search for a suitable landingposition before landing, so as to prevent itself from toppling overresulted from the larger level drop while being landing. After findingthe suitable landing position, the UAV of the present invention willobtain a height information of the landing position, and then adjust thelanding gears in accordance with the height information, and finallyland on the landing position. Therefore, the UAV can prevent fromtoppling over resulted from late calculation of gravity. Moreover, inthe step of correspondingly adjusting the landing gears in accordancewith the height information, the relative distances of the landing gearsrelative to the landing position are made all the same. Thus, when theUAV is controlled to land in a straightly downward way, the landinggears can not only touch the ground simultaneously to keep the balance,but also prevent itself from toppling over in the case that any landinggears have not touched the ground while being landing.

While the invention has been described by way of example and in terms ofthe preferred embodiment(s), it is to be understood that the inventionis not limited thereto. On the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

What is claimed is:
 1. A landing method for an unmanned aerial vehicle(UAV) having a plurality of landing gears, comprising: obtaining a depthimage of a scene; determining a landing position in accordance with thedepth image; obtaining a height information of the landing position;adjusting a plurality of relative distances of the landing gearsrelative to the landing position in accordance with the heightinformation to make the relative distances substantially the same; andlanding the UAV on the landing position.
 2. The landing method accordingto claim 1, wherein the step of obtaining the depth image of the scenecomprises: capturing a 2D image of the scene; dividing the 2D image intoa plurality of regions; obtaining depth values of all pixels in each ofthe regions; and calculating average depth values respectivelycorresponding to each of the regions to obtain the depth image.
 3. Thelanding method according to claim 2, wherein the step of determining thelanding position in accordance with the depth image comprises: obtaininga maximum average depth value and a minimum average depth value from theaverage depth values of the regions, and subtracting the minimum averagedepth value from the maximum average depth value to obtain a differencevalue; and determining whether the difference value is smaller than athreshold value; wherein when the difference value is smaller than thethreshold value, a determination is made to land on the landingposition; wherein when the difference value is larger than the thresholdvalue, a determination is made to re-perform the step of obtaining adepth image of a scene to search for a suitable landing position.
 4. Thelanding method according to claim 3, wherein the threshold value is amaximum telescopic length of each of the landing gears.
 5. The landingmethod according to claim 2, wherein the step of landing the UAV on thelanding position comprises: aiming each of the landing gears to each ofthe regions correspondingly.
 6. The landing method according to claim 5,wherein the step of obtaining the height information of the landingposition is performed after the step of aiming each of the landing gearsto each of the regions correspondingly.
 7. The landing method accordingto claim 1, wherein the step of adjusting the relative distances of thelanding gears relative to the landing position comprises: lengthening orshortening the length of each of the landing gears respectively inaccordance with the height information to make the relative distancessubstantially the same.
 8. An unmanned aerial vehicle (UAV), comprising:a fuselage; a plurality of landing gears disposed in the fuselage; a 3Dimage recognition system disposed in the bottom of the fuselage forobtaining a depth image of a scene; a processing unit coupled to the 3Dimage recognition system for determining a landing position inaccordance with the depth image; and a plurality of distance sensingunits respectively disposed in the landing gears for obtaining a heightinformation of the landing position; wherein the processing unit adjustsa plurality of relative distances of the landing gears relative to thelanding position in accordance with the height information to make therelative distances substantially the same, and lands the UAV on thelanding position.
 9. The UAV according to claim 8, wherein the 3D imagerecognition system captures a 2D image of the scene, divides the 2Dimage into a plurality of regions, obtains depth values of all pixels ineach of the regions, and calculates average depth values respectivelycorresponding to each of the regions to obtain the depth image.
 10. TheUAV according to claim 9, wherein the processing unit obtains a maximumaverage depth value and a minimum average depth value from the averagedepth values of the regions, subtracts the minimum average depth valuefrom the maximum average depth value to obtain a difference value, anddetermines whether the difference value is smaller than a thresholdvalue; wherein when the difference value is smaller than the thresholdvalue, the processing unit determines to land the UAV on the landingposition; wherein when the difference value is larger than the thresholdvalue, the processing unit determines the 3D image recognition system tore-obtain a depth image of a scene to search for a suitable landingposition.
 11. The UAV according to claim 10, wherein the threshold valueis a maximum telescopic length of each of the landing gears.
 12. The UAVaccording to claim 9, wherein the processing unit aims each of thelanding gears to correspond to each of the regions.
 13. The UAVaccording to claim 12, wherein the distance sensing units are infraredsensors.
 14. The UAV according to claim 8, wherein the processing unitlengthens or shortens the length of each of the landing gearsrespectively in accordance with the height information to make therelative distances substantially the same.
 15. A landing method for anunmanned aerial vehicle (UAV) having a plurality of landing gears,comprising: searching for a landing position; obtaining a heightinformation of the landing position; lengthening or shortening thelength of each of the landing gears respectively in accordance with theheight information; and landing the UAV on the landing position.
 16. Thelanding method according to claim 15, wherein in the step of lengtheningor shortening the length of each of the landing gears respectively inaccordance with the height information, a plurality of relativedistances of the landing gears relative to the landing position areadjusted to be equal to each other.
 17. The landing method according toclaim 15, wherein in the step of landing the UAV on the landingposition, the landing gears land on the landing position simultaneously.18. The landing method according to claim 15, wherein the step ofsearching for the landing position comprises: obtaining a depth image ofa scene; and determining the landing position in accordance with thedepth image.
 19. The landing method according to claim 18, wherein thestep of obtaining the depth image of the scene comprises: capturing a 2Dimage of the scene; dividing the 2D image into a plurality of regions;obtaining depth values of all pixels in each of the regions; andcalculating average depth values respectively corresponding to each ofthe regions to obtain the depth image.
 20. The landing method accordingto claim 19, wherein the step of determining the landing position inaccordance with the depth image comprises: obtaining a maximum averagedepth value and a minimum average depth value from the average depthvalues of the regions, and subtracting the minimum average depth valuefrom the maximum average depth value to obtain a difference value; anddetermining whether the difference value is smaller than a thresholdvalue; wherein when the difference value is smaller than the thresholdvalue, a determination is made to land on the landing position; whereinwhen the difference value is larger than the threshold value, adetermination is made to re-perform the step of obtaining a depth imageof a scene to search for a suitable landing position.